As the cost of diesel engines continues to increase, some engine manufacturers are recognizing an opportunity, in certain applications, to transition away from more expensive diesel engines and towards less expensive spark ignition engines. Spark ignition (SI) engines are sometimes less expensive than diesel engines, because they utilize relatively affordable aftertreatment solutions (e.g., three way catalyst), yet they perform in certain applications just as well as diesel engines.
The ability of an SI engine to approach diesel engine performance resides, at least in part, with combustion system efficiency, which may be largely a function of the in-cylinder charge motion (e.g., tumble) prior to the time of combustion. Without high tumble, there may be poor fuel and air homogeneity; a low total kinetic energy at the time of combustion; slow burn rates; and engine knock, which requires later combustion phasing resulting in poor efficiency. In contrast, a high tumble combustion system can deliver faster and more efficient combustion. High tumble in-cylinder flow is possible when the intake air flow enters the combustion chamber with adequate intensity and focus such that a strong barrel shape flow develops in-cylinder. Then, as the piston travels up, the barrel becomes compressed until finally collapsing into individual areas of turbulent vortices of high kinetic energy, thus creating a desirable combustion environment. Known high tumble SI engines often have complex, expensive cylinder head, intake manifold, and valvetrain designs.